The invention relates to an electronic circuit comprising a data processing circuit for processing a digital signal, which data processing circuit is coupled between a first supply connection terminal and a second supply connection terminal for receiving a supply voltage.
Such an electronic circuit is known from the general prior art. In general, the current consumed by the data processing circuit is dependent on the data content of the digital signal. A certain wiring impedance (ohmic resistance and self-inductance) is always present in series with the supply lines of the data processing circuit. Owing to the presence of this wiring impedance, and owing to the fact that the current consumed by the data processing circuit is dependent on the data content of the digital signal, the data processing circuit is supplied with a voltage which has a data-dependent component. The so-called Power Supply Rejection Ratio of an electronic circuit is always finite, so that distortion of signals will arise in the data processing circuit in dependence on the value of the Power Supply Rejection Ratio. In addition, an undesirable signal crosstalk may arise to other parts of the electronic circuit. Efforts are made in practice to limit this signal distortion and signal crosstalk by designing the data processing circuit such that the Power Supply Rejection Ratio is a maximum. Efforts are further made to minimize the wiring impedance present. These measures, however, are not always sufficient. Moreover, these measures may have the result that the implementation of the data processing circuit is very complicated. It is also possible that such an implementation, in which a high Power Supply Rejection Ratio is sought after, will have a negative impact on other quality aspects.
It is accordingly an object of the invention to provide an electronic circuit with a data processing circuit which does not have the above disadvantages, or at least to a very low degree.
According to the invention, the electronic circuit mentioned in the opening paragraph is for this purpose characterized in that the electronic circuit comprises a current compensation circuit which is coupled between the first supply connection terminal and the second supply connection terminal for receiving the supply voltage, which current compensation circuit in the operational state is controlled from the digital signal such that the sum of the current consumption of the data processing circuit and the current consumption of the current compensation circuit is substantially independent of the data content of the digital signal.
Both the data processing circuits and the current compensation circuit have a current consumption which is data-dependent. The data-dependent component of the current consumption of the current compensation circuit has the same magnitude as the data-dependent component of the current consumption of the data processing circuit. The two said current components, however, are in counter-phase. Since the supply connection points of the data processing circuit and of the current compensation circuit are interconnected by means of a very short wiring, there will be substantially no data-dependent current through the wiring impedances. This is because the data-dependent component of the data processing circuit and the data-dependent component of the current compensation circuit compensate one another. The result of this is that the data processing circuit is supplied with a supply voltage which is substantially independent of the data content of the digital signal. Signal distortion and signal crosstalk are thus avoided, even in the case of a low Power Supply Rejection Ratio of the data processing circuit.
An example of an electronic data processing circuit is a so-called DA converter which converts the digital signal into an analog signal.
Advantageous embodiments of current compensation circuits for use in the electronic circuit according to the invention are specified in claims 3 to 6. An advantageous embodiment of a DA converter for use in an electronic circuit according to the invention is specified in claim 7.